X-ray diffraction based residual stress measurements for assessment of fatigue damage and rejuvenation process for undercarriages of aircrafts

Abstract

Assessment of fatigue damage during the service life of any component is important to ensure its continued integrity and predict the remnant life of the component. This is important to reduce the overall life cycle cost of the components. A component undergoing fluctuating stresses experiences fatigue damage and this is one of the major causes of failure of engineering components. Accumulation of fatigue damage takes place in undercarriages of aircrafts due to fluctuating stresses experienced after each landing. The accumulated fatigue damage has been assessed by carrying out residual stress measurements at stress critical regions of the undercarriages using X-ray diffraction technique. In the undercarriages, high compressive residual stresses are introduced as part of fabrication process, to enhance the fatigue resistance. These compressive residual stresses get redistributed due to the localized plastic deformation and become tensile with the increase in number of landings. The life of the undercarriages is extended by employing a rejuvenation treatment to overcome the surface tensile residual stresses, by first removing the material from stress critical regions, followed by shot peening treatment which introduces surface compressive stresses, thus enabling continued use of the undercarriages. The additional thickness provided at the design stage enables removal of fatigue damaged surface layers without affecting the overall structural integrity. The residual stress redistribution in stress critical regions of the struts of the undercarriages was measured and found to match qualitatively well with the values predicted from FEM based simulations.